said by mepadre:
When at the HoPo last night, I looked at the heater tape and spoke to one of the 'plumbers' at the HoPo (remember when Home Depot used to have knowledgable workers... it seems sometimes now it is whoever can fill out an application although some are still very good). The cables indicate they should not be used on drain pipe (supply only). I expect this is due to a fire hazard if the drain is empty and the heater is running? Comments? Someone with more knowledge than the 'plumber' at the HoPo?
Some are designed only for metal supply lines. Others can work on drain. Freeze Free
specifically mentions plastic drain pipes. It's only 3 watts per foot of cord with a 5' kit available in retail packaging.
Your application would be a little different then a typical drain application as your drain pipe usually would contain water. If indeed it runs a few times a day in winter, I doubt it will evaporate enough between pumps that it would run dry. Installing the heat tape a little below the 90 going outside would also provide additional time before it evaporated off, presuming convection currents in the water were enough to keep the top surface from freezing.
Another option is just to replace the plastic line with a metal one.